Favorite tour business in Barcelona?

Park Guell used to have a guided tour you could sign up for-I found it really good for the cheap price.

Sagrada Familia's audio guide was also excellent. I liked the audio guide as you could move around if it got too crowded.

I very much enjoyed the tour of the Barri Gotic offered by the Barcelona tourist office. The group size was smaller than that of the "free" tour covering a similar area. The modernism tour was also interesting; it doesn't go inside the high-cost Gaudi sites but allowed us about 15 minutes in the modernism museum. Casa Mila and Casa Batllo both have good audio guides.

The Palau de la Musica Catalana has English-language tours.

The Sant Pau modernista site (not by Gaudi but very interesting, and blessedly under-visited) has a good audio guide.

We quite liked the audio tour of La Sagrada Familia, so if you don't want to do a live guide for whatever reason, that is a good option.

Casa Batllo is also very cool--good for families too, I'd say. I think they do both live guides in small groups, and audio tours.

Finally, my partner and I did a tapas tour through Food Lover Tours and loved it. We had a really great guide (I remember from reviews that all the guides had very positive feedback), and the food was truly excellent. Good value for money, and the groups are small so you might be with a few other couples or another family, but probably not more than that. You could probably see about getting a private tour instead if you prefer. This is also a nice way to get a lay of the city, if you schedule it for early in your trip.

The four best-known Gaudi sights in Barcelona (La Sagrada Familia, Parc Guell, Casa Mila/La Pedrera, Casa Batllo) are extremely heavily visited. You should understand that you are highly likely to be part of a mob scene even if you have a private guide at those sights. It may still be worth it to you, but all have good audio guides.